The present invention relates to a method and a device for monitoring a sensor.
A method and a device for monitoring a sensor that measures a pressure variable that corresponds to the pressure of the air entering the internal combustion engine is known from German Published Patent No. 40 32 451. In that publication, various methods and modes of operation for monitoring a boost pressure sensor are described. The output signal of the boost pressure sensor is compared to a reference variable. Used as the reference variable is the output signal of a second boost pressure sensor. In an example embodiment, in certain operating states, for example, in response to small loads and rotational speeds, the output signal of the boost pressure sensor is compared to that of an atmospheric pressure sensor. In stationary operating states, the measured value is compared to a value that is calculated on the basis of the fuel quantity and the engine rotational speed.
Disadvantageous in this mode of operation is the fact that a further sensor is required or the monitoring may only be performed in certain operating states. If these operating states are only seldom achieved, then under certain circumstances long operating phases result in which a defective boost pressure sensor is used.
Because a fault is detected if a change in an operating variable characterizing the quantity of fuel injected does not result in a corresponding change in the output variable of the sensor, reliable detection may be possible, especially in the dynamic operation of the internal combustion engine. As the operating variable characterizing the quantity of fuel injected, various variables may be used. Thus it may be possible to use different torque variables, such as the input torque, drive signals for quantity control elements, or other variables that arise in a controlling arrangement for an internal combustion engine. It may be advantageous to use the mode of operation according to the present invention in a boost pressure sensor which measures the pressure of the air that is fed to the internal combustion engine. The mode of operation, however, may also be used in the case of other sensors.
Certain faults such as the icing up of a sensor only arise in response to specific operating states, so it may be advantageous if the monitoring of the sensor is made to be a function of the presence of certain operating states.
The icing up of the sensor only occurs in certain ranges of the air temperature. The monitoring occurs if a variable that characterizes the air temperature is smaller than a threshold value. Monitoring is only reliable and/or capable of great precision if preestablished rotational speed values and/or fuel quantity values are present. The monitoring occurs if predetermined values exist for the rotational speed and/or the quantity of fuel injected.
It may be advantageous if a substitute value is used in response to a detected fault. One substitute value that may be easy to calculate derives from the rotational speed and the quantity of fuel injected. By using the substitute value, it may be possible to continue to operate the internal combustion engine even in the event of a fault, the control precision of the internal combustion engine is only slightly impaired.
The present invention is discussed below on the basis of the example embodiments depicted in the drawing.